docs: def _skip_to_blank(f, spacegroup, setting):
      """Read lines from f until a blank line is encountered."""
      while True:
          line = f.readline()
          if not line:
              raise SpacegroupNotFoundError(
                  'invalid spacegroup %s, setting %i not found in data base' % 
                  ( spacegroup, setting ) )
          if not line.strip():
              break